The long-term goal of the research is to obtain a Chinese hamster ovary cell line capable of producing human estrogen receptor as a significant amount of its secreted protein. Purified receptor protein may then be used (1) to obtain X-ray crystallographic data on the structure of the receptor to aid in rational anti-estrogen drug design and (2) to be used as a research reagent for the development of estrogen antagonists for treatment of estrogen receptor positive tumors. The specific aim of the proposal is the production of a mammalian cell expression vector capable of encoding a secreted estrogen receptor and the production of CHO cell transfectant pools using this vector. A primary accomplishment of the work proposed will be the invention of expression vectors allowing for the rapid construction and in vitro analysis of any novel secretory protein.